Subscriber Services: Maintain CoS shaping rates for ANCP subscribers across ANCP restarts

When ANCP stops due to a process restart or GRES, CoS now enforces the ANCP downstream shaping-rates until the CoS keepalive timer expires. When the timer expires, CoS reverts to its configured shaping-rate for the interfaces. You can configure the CoS keepalive timer by including the existing maximum-helper-restart-time seconds statement at the [edit protocols ancp] hierarchy level. It specifies how much time other daemons such as CoS will wait for ANCP to restart and is used to configure the CoS rate update keepalive timer. ANCP does not maintain TCP sessions from neighbors across the restart or GRES. When it restarts, it must re-establish sessions with neighbors and subscriber sessions before the timer expires. For all the re-established sessions, ANCP updates CoS with the updated downstream shaping rates and provides DSL line attributes to the session database for AAA. If CoS stops or restarts while ANCP is up, ANCP retransmits all known subscriber downstream rates to CoS. Any existing adjusted shaping rates that have not been updated revert to the configured CoS shaping rates when the CoS restart timer expires.